1. Field of the Invention
This invention relates to improvements in catalytic cracking of hydrocarbon oils and, in particular, is directed to a process for the catalytic cracking of hydrocarbon oils to produce higher gasoline and distillate yields, increase gasoline octane number and reduce the product pour point of the distillates. The cracking catalyst used is a mixture of Zeolite Beta with a conventional faujasite-type zeolite-containing cracking catalyst, such as zeolite Y. The cracking process takes place in the absence of added hydrogen.
2. The Prior Art
Catalytic cracking of hydrocarbon oils utilizing crystalline zeolites is a known process, practiced, for example, in fluid-bed catalytic cracking (FCC) units, moving bed or thermorfor catalytic cracking (TCC) reactors and fixed bed crackers. Crystalline zeolites have been found to be particularly effective for the catalytic cracking of a gas oil to produce motor fuels, and have been described and claimed in many patents, including U.S. Pat. Nos. 3,140,249; 3,140,251; 3,140,252; 3,140,253; and 3,271,418. It is also known in the prior art to incorporate the crystalline zeolite into a matrix for catalytic cracking, and such disclosure appears in one or more of the above-identified U.S. patents.
It is also known that improved results will be obtained with regard to the catalytic cracking of gas oils if a crystalline zeolite having a pore size of less than 7 Angstrom units is included with a crystalline zeolite having a pore size greater than 8 Angstrom units, either with or without a matrix. A disclosure of this type is found in U.S. Pat. No. 3,769,202. Although the incorporation of a crystalline zeolite having a pore size of less than 7 Angstrom units into a catalyst composite comprising a large pore size crystalline zeolite (pore size greater than 8 Angstrom units) has indeed been very effective with respect to raising the octane number; nevertheless, it did so at the expense of the overall yield of gasoline.
Improved results in catalytic cracking with respect to both octane number and overall yield were achieved in U.S. Pat. No. 3,758,403. In the '403 patent, the cracking catalyst comprised a large pore size crystalline zeolite (pore size greater than 7 Angstrom units) in admixture with a ZSM-5 type zeolite, wherein the ratio of ZSM-5 type zeolite to large pore size crystalline zeolite was in the range of 1:10 to 3:1. Effective cracking processes were disclosed as being achieved when the catalyst was used to obtain the inherent advantages realized in moving bed techinques, such as the Thermofor Catalytic Cracking Process (TCC), as well as in fluidized cracking processes (FCC).
The use of ZSM-5 type zeolite in conjunction with a zeolite cracking catalyst of the X or Y faujasite variety is described in U.S. Pat. Nos. 3,894,931; 3,894,933; and 3,894,934. The two former patents disclose the use of a ZSM-5 type zeolite in amounts of about 5-10 wt %; the later patent discloses the weight ratio of ZSM-5 type zeolite to large pore size crystalline zeolite within the range of 1:10 to 3:1.
The addition of a separate additive or composite catalyst comprising one or more members of the ZSM-5 type has been found to be extremely efficient as an octane and total yield improver, when used in very small amounts, in conjunction with a conventional cracking catalyst. Thus, in U.S. Pat. No. 4,309,279, it was found that only 0.1 to 0.5 wt % of a ZSM-5 type catalyst, added to a conventional cracking catalyst under conventional cracking operations, could increase octane by about 1-3 RON+O (Research Octane Number Without Lead).
U.S. Pat. No. 4,309,280 also teaches ZSM-5 and other zeolites in conjunction with a conventional cracking catalyst.